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On some new species of Trigonia from the Inferior Oolite of t/te 

 Cotteswolds, with preliminary Remarks upon that Genus. By 

 John Lycett, Esq. 



Read 19th July 1853. 



" Not only by their numbers, but still more by the richness of their spe- 

 cific divisions, by the peculiar prominence of individualization, do the 

 species of the remarkable genus Trigonia attain their maximum point in 

 the lower chalk." — L. von Buch, Betrachtungen uber die Verbreituny uml 

 die Grenzen der Kreide Bildungen. Bonn, 1849. 



Trigonia and Pholadomya are the two organic forms winch 

 pre-eminently serve to impress a distinctive character upon the 

 Testacea of the Oolite rocks in whatever countiy they are dis- 

 covered, and accordingly from the time when fossil shells were 

 regarded as mere freaks of nature, we find that authors depicted 

 their Hippocephaloides and Bucardites. But conspicuous as is 

 the position which Trigonia holds throughout the Oolites, the 

 quotation above chosen, and the passages which immediately 

 follow, are not the less true and worthy of notice ; they evince 

 the strong impression made upon the mind of a distinguished 

 and veteran palaeontologist by the remarkable prominence which 

 the genus Trigonia holds amongst the Cretaceous Conchifera, 

 both in its numbers and world-wide distribution, a prominence 

 which appears not the less remarkable when we remember that 

 the leading sectional oolitic forms of the genus had already 

 nearly disappeared, and that a little higher in the series even the 

 cretaceous forms exhibit a rapid diminution, until in the upper 

 chalk a trifling remnant alone remains to indicate the forth- 

 coming extinction of the fossil Trigonia , a loss which is not the 

 less strongly felt upon a contemplation of the altered, and in 

 some measure degenerated characters of the living species. 

 But if the attributes claimed for the genus at the aera which im- 

 mediately precedes the extinction of the Cretaceous species are 

 well-founded, it will, I think, appear equally evident that at its 

 primal sera in the earlier portion of the Oolitic system the genus 

 had already acquired that prominence amongst the Testacea 

 which Von Buch has so vividly described, and that the forms, 

 dimensions, and ornamentations of the species were scarcely less 

 characteristic and varied. Upon numbering the entire recorded 



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